1. Field of the Invention
The present invention relates to a process of production and purification of condensed bromoacenaphthylene.
2. Description of the Prior Art
In recent years for precautions against fire, it has been a widely adopted practice that various inflammable resins, such as polyethylene, polypropylene and ethylenepropylene rubbers are made non-flammable and for this purpose a method is known, which comprises adding various flame retarders to the resins. Further, it has been an extreme necessity that electric cables and various instruments used in nuclear or breeder reactors and ionization radiation generators etc. are non-flammable for security and safety. Therefore, various materials employed for the cables and instruments, such as insulating coating materials and many kinds of resin compositions, are required to be radiation resisting as well as non-flammable.
Condensed bromoacenaphthylene is a compound having excellent non-flammable and radiation resisting properties. The double bond in the molecule of the compound facilitates grafting to resins by treatment for radical generation. Also by virtue of its nature as a condensate, the compound has excellent miscibility with resins, because it does not breed on the surface of resins or it is not lost by volatilization for a long run. Thus the compound is capable of maintaining non-flammable and radiation resisting properties for a long period (Japanese Laid-Open Patent Application No. Sho 56-122862).
For the production of condensed bromoacenaphthylene, two processes have been proposed; one proposal uses iron (III) chloride as catalyst and bromination is carried out with bromine 6 times as much as acenaphthene at a temperature between 20.degree. and 30.degree. C. (Morita and Hagiwara: The 30th High Molecular Conference, G3A14, Tokyo(1981)), and the other proposal treats brominated acenaphthene in which bromine has been introduced at the arylic and benzylic positions in the presence of a catalyst for the synthesis (Japanese Laid-Open Patent Application No. Sho 56-122862).
The former process, however, has been found to be accompanied with a lower yield, because a significant amount of polybrominated monomers is produced as by-product. According to the latter proposal, which proposes condensation of, for example, 1,2,3,5-tetrabromoacenaphthene in the presence of a catalyst, the carbon atom at the benzylic position at which a bromine atom is attached is so highly reactive as readily to give rise to the Friedel-Crafts type of alkylation reaction in the presence of a Lewis acid catalyst, so that one cannot control the degree of condensation. As a result, bromine atoms are significantly lost at the benzylic positions and subsequent dehydrobromination reaction can produce only a reduced number of double bonds than otherwise. Further, the starting material, brominated acenaphthene in which bromine has been introduced at the arylic and the benzylic positions, can be produced in a troublesome and hard way with only a low yield, when commercially available acenaphthene is used as the first starting material.
Meanwhile, condensed bromoacenaphthylene, which has been produced from acenaphthene by bromination and condensation followed by dehydrobromination reactions, usually contains minute amounts of derivatives as impurities which are objectionable in practical treatment and usage.
The impurities are absorbed on the surface, and contained in the bulk of the condensate and they cannot be easily removed therefrom by the ordinary filtration, washing and reprecipitation. This fact caused practical drawbacks often encountered in operations. For example, the condensed bromoacenaphthylene adheres onto a roll surface when kneaded with a resin using a roller and, in the case of a shaped composition, the condensed bromoacenaphthylene breeds like pollen on the surface of the resin. Further its adverse effects are observed on tensile strength, elongation, and water-proofness at high temperatures.
With these problems in mind, the present inventors intensively investigated for a process for production and purification of condensed bromoacenaphthylene from acenaphthene as starting material, and the following facts have been found.
(1) Bromination of acenaphthene carried out at a temperature between 5.degree. and 55.degree. C. using a Lewis acid catalyst produces brominated acenaphthene and condensate thereof which are brominated only at the arylic position, and not at the benzylic position. PA1 (2) Bromination reaction of acenaphthene with elemental bromine in the presence of a radical initiator produces a compound which is brominated at the benzylic position. Then if the bromination reaction is continued with added bromine and a Lewis acid catalyst for accelerating bromination at the arylic position, a compound with an extremely high degree of condensation is obtained, but a benzylically brominated compound is difficult to obtain. PA1 (A) a step of treatment in which acenaphthene is brominated with bromine and condensed in a halogenated hydrocarbon in the presence of a Lewis acid catalyst; PA1 (B) a step of treatment in which the Lewis acid catalyst is removed and bromination reaction with bromine was continued with a radical initiator added; and PA1 (C) a step of treatment in which the dehydrobromination reaction is carried out. PA1 (B) a step of removing the Lewis acid catalyst and then continuing the bromination with bromine with an added radical initiator; and PA1 (C) a step of carrying out dehydrobromination reaction (hereinafter called the basic process).
Further investigation revealed that condensed bromoacenaphthylene can be produced by following treatments:
It has been further found that a condensate which is brominated not only at the arylic position but also at the benzylic position can be produced, though in a small amount, only when bromination of acenaphthene is carried out with bromine at least 3 times as much in moles as acenaphthene at a temperature between 5.degree. and 55.degree. C. using iron catalysts as the Lewis acid catalysts.
Therefore, more investigation has been made to reveal a surprising fact, that when bromination and condensation of acenaphthene is carried out in a halogenated hydrocarbon solvent at a temperature of 60.degree. C. or higher in the presence of iron catalyst using bromine at least 3 times as much in moles as acenaphthene, an acenaphthene condensate which is brominated at the benzylic position is obtained with a satisfactorily high yield.
Meanwhile, the condensed bromoacenaphthylene which is produced by the bromination, condensation and dehydrobromination reactions of acenaphthene can be purified by dissolving the condensate in an organic solvent and bringing it in contact with an appropriate amount of an inorganic oxide, an alkaline earth metal salt or amorphous carbon, thus selectively removing by adsorption of those minute impurities which cause the adherence on rollers and the breeding, and hence assuring successful production of a resin composition from the condensed bromoacenaphthylene with improved physical properties.